Jealous boyfriend jailed for stalking, stabbing ex-girlfriend in her home

A jealous teenager who stalked his ex-girlfriend and broke into her Adelaide home, where he attacked her and her new boyfriend with a knife, has been sentenced to more than four-and-a-half years' jail.

The District Court heard the man, who was 19 at the time, became "obsessed" and "fixated" with his ex-girlfriend and her new relationship.

In July last year, after stalking her, sending multiple text messages and following her home from work to find out where she lived, the teenager broke into her house in the early hours of the morning.

The man's ex-girlfriend woke up when she felt her pillow being pulled from underneath her head.

After turning on the light the woman and her new boyfriend, who was sleeping next to her, saw the man crouched down next to her side of the bed wearing black clothes and a balaclava.

"She screamed and her boyfriend jumped across the bed and tackled you to the floor," Judge Paul Muscat said.

The court heard during the struggle the woman and her new boyfriend were both stabbed, with the woman suffering a punctured lung.

The woman's boyfriend still managed to pull off the teenager's balaclava and recognised him.

Teen 'downloaded floorplan before break-in'

Judge Paul Muscat said it was serious offending motivated by jealousy, and he rejected the man's claims he never intended to hurt anyone.

"The text messages you sent your ex-girlfriend are revealing, you were plainly feeling rejected, jealous and angry after she left you and especially after you discovered she was involved with another boy," Judge Muscat said.

"Disturbingly you had even downloaded a floor plan of that house from a website."

The man pleaded guilty to aggravated serious criminal trespass in a place of residence, aggravated causing harm with intent and aggravated recklessly causing harm.

Judge Muscat noted the teenager had not shown any signs of a violent disposition before the attack

A forensic psychologist reported the behaviour seemed out-of-character, and said the man was suffering from an adjustment disorder and depression at the time.

"The psychologist suggested that your offending behaviour is best described as a crime of passion motivated by biblical themes of jealousy, revenge, envy, rejection and anger," Judge Muscat said.

"However your criminal behaviour is characterised, the reality is you are unable to accept that your girlfriend ended her relationship with you.

"There followed a period of harassing her, seeking answers and you became obsessed with wanting to know who she was with and whether she had slept with her new boyfriend and whether she had cheated on you.

"As the psychologist stated you then became fixated with wanting to confront your ex-girlfriend and her new boyfriend and you most certainly did that in the most terrifying and frightening of circumstances."

Offender 'no longer angry, hostile'

The psychologist said he believed the accused was "no longer the angry, hostile young man" he was in the lead-up to the attack, and with comprehensive rehabilitation programs his likelihood of reoffending would be low.

But Judge Muscat said the case involved serious offences and he could find no good reason to suspend the sentence.

The court heard the offender, now 20, had since reflected on his crimes while in custody and was shocked by his own conduct and felt remorseful.

It heard the ex-girlfriend remained "petrified" that he would seek to hurt her in future and suffered severe psychological distress including anxiety and depression.

"You have scarred her both physically and emotionally. She is no longer the same and tragically may never be so again."

After allowing discounts for the offender's guilty pleas, Judge Muscat imposed a total sentence of four years, eight months and 12 days with a non-parole period of two years and three months.

With time already served, the man will be eligible for parole in October next year.